使用malloc的struct的内存分配，其中一个数据条目是指针

I understand the difference between memory allocation using malloc for an array of struct and for an array of pointers to struct. But I want to assign memory using malloc for an array of struct, in the case that the struct itself contains a pointer to another struct. Here is the code for what I am trying to do:

我理解使用malloc为struct数组和struct指向数组的内存分配之间的区别。但是我希望使用malloc为struct数组分配内存,在struct本身包含指向另一个struct的指针的情况下。这是我想要做的代码:

#include<stdio.h>
#include<stdlib.h>

typedef struct linkedlist {
    int pCol;
    struct linkedlist *next;
} plist;

typedef struct particle {
    int color;
    double rad;
    double rx;
    double ry;
    double vx;
    double vy;
    struct linkedlist *event;
} state;

int main()
{
    int N = 5, w = 4;

    plist *ls = (plist*)malloc((N+w)*sizeof(plist));
    printf("N=%d, w=%d, sizeof state=%d, total=%d, sizeof discs=%d\n\n",
    N,w,sizeof(plist), (N+w)*sizeof(plist), sizeof(ls));

    state *discs = (state*)malloc((N+w)*sizeof(state));
    printf("N=%d, w=%d, sizeof state=%d, total=%d, sizeof discs=%d\n",
    N,w,sizeof(state), (N+w)*sizeof(state), sizeof(discs));
    return 0;
}

When I run this, I get the following output:

当我运行它时,我得到以下输出:

N=5, w=4, sizeof plist=8, total=72, sizof ls=4

N=5, w=4, sizeof state=56, total=504, sizof discs=4

So, I want to know why does the ls or the discs get assigned only 4 bytes and how can I get total memory required assigned for these arrays of structs?

所以,我想知道为什么ls或光盘只被分配4个字节,我怎样才能获得为这些结构数组分配的总内存?

2 个解决方案

#1

You are printing size of pointer(ls) and not size of datatype/structrure pointed by the pointer (*ls).

您正在打印指针(ls)的大小,而不是指针指向的数据类型/ structrure的大小(* ls)。

Do sizeof(*ls) and sizeof(*discs) in your printf statements if you intend to find size of plist and state because that is where ls and discs point to.

如果您打算查找plist和state的大小,请在printf语句中执行sizeof(* ls)和sizeof(* disc),因为这是ls和disc指向的位置。

If you are thinking of printing the total size allocated to ls or discs by malloc. That is not possible. Its not going to print ((N+w)*sizeof(plist)). So even doing sizeof(*ls) is not going to tell you how many plist structures you allocated

如果您正在考虑通过malloc打印分配给ls或光盘的总大小。这是不可能的。它不会打印((N + w)* sizeof(plist))。所以即使做sizeof(* ls)也不会告诉你你分配了多少个plist结构

#2

in your code, ls is of type plist *,.i.e., a pointer.

在你的代码中,ls是plist *类型,即指针。

sizeof() is an operator which returns the size of the data type, not the amount of memory allocated.

sizeof()是一个运算符,它返回数据类型的大小,而不是分配的内存量。

Same goes for discs.

光盘也一样。

#1